Obtaining tissue samples for diagnostic purposes is a commonly performed surgical procedure known as a biopsy. Such a procedure requires two steps: cutting a tissue specimen and then retrieving the cut tissue specimen. Electrosurgical devices are well-known surgical instruments which have been used in biopsy procedures for coagulation the tissue removal site. Coagulation of the tissue occurs with electrocoagulating instruments including at least one conductive electrode. Radio frequency (RF) energy is conducted through this electrode to either a remote conductive body plate (monopolar) or to a second, closely spaced conductive electrode (bipolar). Current passing through the space between the two electrodes will coagulate the blood and other body fluids placed between them.
In bipolar electrosurgical instruments, the two electrodes are closely spaced to one another, usually at the distal end of an instrument handle. The return path is very short and only involves the tissue and fluids in a short path between the two electrodes. Electrosurgical devices can also cut tissue by applying a voltage across two electrodes causing an arc discharge which creates such a high heat energy that the cells comprising the tissue are desicated.
A bipolar electrosurgical biopsy instrument where the two tissue specimen collecting members mechanically cut the tissue specimen and are also electrically insulated from one another and comprise the bipolar electrodes for electrocoagulation are known. Metal-to-metal contact along sharpened edges of cutting electrode surfaces of a bipolar instrument can result in an electrical short. Furthermore, the attempt to use a rivet or a screw as the pivot point for the biopsy tissue specimen collecting receptacles is another area where short-circuiting is likely to occur. When such a short exists, the electrical current does not flow through the body or tissue to effect coagulation, but instead, follows the short circuit path from one electrode to another. Additionally, the histological integrity of the tissue specimen is not always maintained when electrodes are used for both cutting of the tissue specimen and coagulation of the removal site.
Certain bipolar instruments have been developed incorporating metal cutting surfaces which also act as electrodes. For example, bipolar scissors have been developed with blades at the distal tip performing coagulation and cutting of the tissue with a mechanical shearing action. The two blades are effectively insulated from one another, allowing them to function as bipolar electrodes for electrocoagulating small blood vessels in the surgical field. U.S. Pat. No. 5,352,222 discloses such a surgical scissors with bipolar coagulation features. While surgical scissors are utilized in a coagulation and cutting operation, a need exists for a single instrument to be used in biopsy procedures which require coagulation, cutting and intact removal of the tissue specimen. In the past, biopsy procedures often have required an exchange of instruments to perform these steps.
A need, therefore, exists for a single bipolar electrosurgical biopsy device where the coagulating electrodes are in close proximity to the mechanical cutting surfaces (since they are both located on the tissue specimen collecting receptacles) and yet, isolates the tissue specimen from the electrodes to maintain histological integrity.